A liquid metal ion gun includes a liquid metal ion source (hereinafter referred to as LMIS) arranged in a vacuum container. The liquid metal ion gun emits an ion beam corresponding to an amount of ion emission (emission current) responsive to voltages by thermally energizing the emitter (electrode) of the LMIS through a high-voltage cable or applying a high voltage (extraction voltage) across parts of an extracting electrode. The ion beam that is emitted from the LMIS is received by a beam limiting aperture, which limits the emission current and spreading of the ion beam that will propagate toward the downstream side of the beam limiting aperture.
For the aforementioned liquid metal ion gun, for example, a gallium liquid metal ion gun, emission stability is maintained when the balance between the amount of gallium consumed by an emitter for ion irradiation purpose and the amount of gallium supplied to the emitter from a reservoir is kept, i.e., when the amount of consumed gallium is in equilibrium with the amount of supplied gallium.
However, if a foreign material mixes with gallium, then such a foreign material functions to inhibit gallium from being supplied, or the purity of the gallium is changed and the liquid metal suffers from changes in physical properties. As a result, the amount of consumed gallium is not in equilibrium with the amount of supplied gallium, which will lead to reduction in emission stability.
One example of the foreign material that will be mixed in the liquid metal of the LMIS is particles (sputtered particles) generated while the beam limiting aperture is irradiated and sputtered with the ion beam.
A conventional technique for suppressing the mixing of the sputtered particles in the liquid metal of the LMIS is described in Patent Document 1. The technique described in Patent Document 1 is as follows. A degradation in stability of an ion current is suppressed in such a manner that a part that is included in the beam limiting aperture and irradiated with the ion beam is constituted by a sintered body having low-melting-point metal mixed therein and the sputtered particles are melted in the liquid metal so as not to form a slag.
In addition, the following technique is also known. In the technique, metal that is the same type as the liquid metal of the LMIS is used for a protective diaphragm (refer to Patent Document 2 and the like). Furthermore, the following technique is also known. In the technique, the surface or all parts of an emitter electrode are made of molten metal used for the tip of the emitter electrode or made of one or more types of metal constituting an alloy used for the tip of the emitter electrode (refer to Patent Document 3 and the like).
In addition, the following technique is also known. In the technique, a beam limiting aperture that includes, as a base material, the same metal as the emitter (electrode) of the LMIS is formed, and accumulated liquid metal that is the same as the LMIS is provided in a region that is irradiated with the ion beam (refer to Patent Document 4 and the like). Furthermore, the following technique is also known. In the technique, the liquid metal of the LMIS is placed in a container having a recessed portion that includes an aperture hole in the lowest surface, while the ion beam passes through the aperture hole (refer to Patent Document 5 and the like).